# Kelvin-Froude wake patterns of a traveling pressure disturbance

## TL;DR

This paper investigates how finite size and shape of pressure disturbances affect Kelvin wake patterns on deep water, revealing new regimes and classifications based on the Froude number and boundary sharpness.

## Contribution

It generalizes Kelvin's wake theory to finite and arbitrary pressure sources, introducing characteristic Froude numbers and classifying wake patterns accordingly.

## Key findings

- Wake patterns depend on Froude number and disturbance shape.
- Existence of two critical Froude numbers, F1 and F2, for wake presence.
- Sharp boundary sources produce interference effects and complex wake structures.

## Abstract

According to Kelvin, a point pressure source uniformly traveling over the surface of deep calm water leaves behind universal wake pattern confined within $39^{\circ}$ sector and consisting of the so-called transverse and diverging wavefronts. Actual ship wakes differ in their appearance from both each other and Kelvin's prediction. The difference can be attributed to a deviation from the point source limit and for given shape of the disturbance quantified by the Froude number $F$. We show that within linear theory effect of arbitrary disturbance on the wake pattern can be mimicked by an effective pressure distribution. Further, resulting wake patterns are qualitatively different depending on whether water-piercing is present or not ("sharp" vs "smooth" disturbances). For smooth pressure sources, we generalize Kelvin's stationary phase argument to encompass finite size effects and classify resulting wake patterns. Specifically, we show that there exist two characteristic Froude numbers, $F_{1}$ and $F_{2}>F_{1}$, such as the wake is only present if $F\gtrsim F_{1}$. For $F_{1}\lesssim F \lesssim F_{2}$, the wake consists of the transverse wavefronts confined within a sector of an angle that may be smaller than Kelvin's. An additional $39^{\circ}$ wake made of both the transverse and diverging wavefronts is found for $F\gtrsim F_{2}$. If the pressure source has sharp boundary, the wake is always present and features additional interference effects. Specifically, for a constant pressure line segment source mimicking slender ship the wake pattern can be understood as due to two opposing effect wakes resembling (but not identical to) Kelvin's and originating at segment's ends.